Clock



FIG. 1 is a front plan view of my ornamental design for a clock, wherein the broken lines shown in the figure are for illustrative purposes only and not a part of the claimed design.

FIG. 2 is a top view of the design;

FIG. 3 is a back view of the design; and,

FIG. 4 is a side view of the design. 

The ornamental design for a clock, as shown and described. 